Method for Removing a Sealing Plug from a Well

ABSTRACT

A method for removing a sealing plug from a casing or a wellbore according to which a sealing plug is adapted to expand into engagement with the casing or the wellbore. A wireless signal is sent to the plug to cause the plug to lose its structural integrity and fall to the bottom of the wellbore.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application claiming Priority to U.S. patentapplication Ser. No. 11/489,853, filed Jul. 20, 2006 and entitled“Method for Removing a Sealing Plug from a Well,” which is incorporatedby reference herein in its entirety.

BACKGROUND

This application relates to a method for removing a sealing plug from acasing or a wellbore in oil and gas recovery operations.

After a well is put into production, a wellhead is usually placed overthe well at the ground surface and a closure device, such as a sealingcap, or the like, is provided at the wellhead to prevent the flow ofproduction fluid from the well during certain circumstances. Sometimes,under these conditions, the closure device must be removed forreplacement, repair, etc., which creates a risk that some productionfluid from the well may flow out from the upper end of the well.

To overcome this, a sealing plug, also referred to as a packer, bridgeplug or barrier plug, is usually inserted in the well and activated toplug, or seal, the well and prevent any escape of the production fluidout the top of the well. However, when it is desired to recap the well,the plug must be removed. One common technique for removing the plug isto employ a rig that is used to drill-out the sealing plug, or pull theplug from the well. However, this technique requires sophisticatedequipment, is labor intensive, and therefore is expensive.

Another technique to remove the plug from the well is to implant atiming device in the plug to actuate an explosive in the plug after apredetermined time. However, this type of technique has drawbacks since,after these types of plugs have been set in the well, the operator maywant to extend the life of the plug from the predetermined time to alonger period of time or even an indeterminate time, and to do so wouldnot be possible.

Therefore, what is needed is a sealing plug of the above type which canbe placed in the well to seal off the flow of production fluid asdiscussed above and yet can be removed at an indeterminate time in arelatively simple and inexpensive manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic/elevational/sectional view of an oil and gasrecovery operation including a sealing plug according to an embodimentof the invention.

FIG. 2 is an enlarged, sectional view of the plug of FIG. 1.

FIG. 3 is a view, similar to that of FIG. 1, but depicting a differentoperational mode.

DETAILED DESCRIPTION

Referring to FIG. 1, the reference numeral 10 refers to a wellborepenetrating a subterranean formation for the purpose of recoveringhydrocarbon fluids from the formation. The wellbore 10 could be an openhole completion or a cased completion, and in the latter case a casing12 would be cemented in the wellbore 10 in a conventional manner.

A sealing plug, or sealing tool, 14 is disposed in the wellbore 10 at apredetermined depth and is lowered to this position by a work string 16,in the form of coiled tubing, jointed tubing, wire line, or the like,which is connected to the upper end of the plug 14. The plug 14 is showngenerally in FIG. 1 and will be described in detail later.

The work string 16 extends from a rig 18 located above ground andextending over the wellbore 10. The rig 18 is conventional and, as such,includes a support structure, a motor driven winch, or the like, andother associated equipment for lowering the plug 14, via the string 16,into the wellbore 10.

The string 16 extends through a wellhead 22 that is positioned over theupper end of the wellbore 10 and the casing 12 at the rig 18. Thewellhead 22 is conventional and, as such, includes a closure device (notshown), such as a cap, or the like, for preventing the flow ofproduction fluid from the formation through the casing 12, whilepermitting movement of the string 16, in a conventional manner.

When the well is not in production, the above-mentioned closure deviceassociated with the wellhead 22 is set to prevent any flow of productionfluid from the formation and through the casing 12 to the rig 18.However, if the closure device has to be removed for repair,replacement, or the like, the casing 12 must be sealed to prevent theproduction fluid flow. To this end, the plug 14 is lowered, via thestring 16, to a desired depth in the casing 12 adjacent to, or above,the formation, such as to the depth shown in FIG. 1, and the plug 14 isset in the casing 12 in a manner to be described.

With reference to FIG. 2, the plug 14 includes a mandrel 30 having anupper end 30 a that is connectable to the lower end of the string 16 inany conventional manner. The mandrel 30 has a lower end 30 b, and acontinuous bore extends between the upper end 30 a and the lower end 30b.

A tubular liner 32 is disposed in the bore of the mandrel 30, with thelower end of the liner 32 extending flush with the lower end 30 b of themandrel 30. A cap 34 extends over the lower end 30 b of the mandrel 30and the corresponding end of the liner 32 to retain the liner 32 in themandrel 30.

A series of axially-spaced circumferential grooves 32 a are formed inthe outer surface of the liner 32 which receive a detonation cord 35that extends around the liner 32. The detonation cord 35 is of aconventional design and, as such, can be a thin, flexible, waterprooffabric tube with a highly explosive core that can transmit a detonationwave. The cord 35 is wrapped around the liner 32 and extends in thegrooves 32 a, and also is more tightly wrapped in an enlarged recess 32b formed in the liner 32. A conventional detonation initiator 38 abutsthe upper end of the liner 32, and, when activated in a manner to bedescribed, detonates the cord 35, causing the explosive in the cord toexplode.

A compression-set, annular sealing element 44 extends around the mandrel30 and is axially positioned between two sets of extrusion limiters 48 aand 48 b. A pair of wedges 50 a and 50 b extend between the extrusionlimiters 48 a and 48 b, respectively, and two sets of slips 52 a and 52b, respectively. The inner surfaces of the end portions of the slips 52a and 52 b adjacent the wedges 50 a and 50 b are beveled so as toreceive the corresponding tapered end portions of the wedges 50 a and 50b. The sealing element 44 can be fabricated from a conventional materialthat performs the sealing function to be described, and the slips 52 aand 52 b and the mandrel 30 are preferably fabricated from a frangiblematerial.

A mechanism for expanding and setting the sealing element 44 and theslips 52 a and 52 b includes a pair of axially-spaced ratchet shoes 54 aand 54 b that extend around the mandrel 30 and abut the correspondingends of the slips 52 a and 52 b. Since the extrusion limiters 48 a and48 b, the wedges 50 a and 50 b, the slips 52 a and 52 b, and the shoes54 a and 54 b are conventional, they will not be described in furtherdetail.

The sealing element 44 and the slips 52 a and 52 b are activated, orset, in a conventional manner by using a setting tool, or the like (notshown), to move the shoe 54 a downwardly relative to the mandrel 30, asviewed in FIG. 2, and to move the shoe 54 b upwardly relative to themandrel 30. This places a compressive force on the assembly formed bythe slips 52 a and 52 b, the wedges 50 a and 50 b and the sealingelement 44. As a result, the slips 52 a and 52 b are forced radiallyoutwardly into a locking engagement with the inner wall of the casing12, and the sealing element 44 expands radially outwardly into a sealingengagement with the inner wall of the casing 12. Thus, the plug 14 sealsagainst any flow of production fluid from the formation through thewellbore 10. After the plug 14 is set in the above manner, the string 16(FIG. 1) is disconnected from the plug 14 in any conventional manner,and the string 16 is brought to the ground surface by the winch of therig 18.

When it is desired to recap the well, the plug 14 is removed in thefollowing manner. Referring to FIG. 3, an actuator 60 is connected tothe leading end of the string 16 in any conventional manner. The string16 is then lowered into the wellbore 10 until the actuator 60 extendsabove, and in proximity to, the plug 14 and, more particularly, theinitiator 38 (FIG. 2). The actuator 60 is adapted to transmit, and theinitiator 38 is adapted to receive, a wireless signal, or code, foractivating the initiator 38. In particular, the actuator 60 includes atransmitting antenna (not shown) that is adapted to transmit the signalto the initiator 38, and the initiator 38 includes a receiving antennathat receives the transmitted signal from the actuator 60. The signaltransmitted between the actuator 60 and the initiator 38 is adapted toactivate the initiator 38 and can be of any conventional type, such aselectrical, acoustical, or magnetic.

The activation of the initiator 38 by the above signal detonates thecord 35 and explodes the explosive associated with the cord 35. Theexplosion disintegrates, or breaks up at least a portion of the plug 14and releases the engagement of the plug 14 with the casing 12 or thewellbore 10. The resulting fragments of the plug 14 fall to the bottomof the wellbore 10 by gravity. The string 16 (FIG. 3), with the actuator60, is then brought to the ground surface by the winch of the rig 18(FIG. 1).

The above-mentioned closure device associated with the wellhead 22 isthen reinstalled over the wellhead 22 and set to prevent any flow ofproduction fluid from the formation and through the wellbore 10 to therig 18.

Thus, the plug 14 can be placed in the wellbore 10 and activated to sealoff the flow of production fluid as discussed above and yet can beremoved in a relatively simple and inexpensive manner at anyindeterminate time.

According to an alternate embodiment, the initiator 38 responds to thesignal from the actuator 60 and produces heat and oxygen in a manner tobe described, and one or more of the components of the plug 14 areformed from a consumable material that burns away and/or losesstructural integrity when exposed to the heat and oxygen.

In particular, the initiator 38 includes what is commonly referred to asan “exploding bridge wire” that is surrounded by a material thatproduces heat and oxygen when ignited by the wire. In particular thebridge wire consists of a wire that is connected across a source ofhigh-voltage electricity so that when activated, the resulting highcurrent generates heat in the wire that is transferred to, and issufficient to ignite, the material. An example of such a material isthermite, which comprises iron oxide, or rust (Fe₂O₃), and aluminummetal powder (Al). When ignited and burned, the thermite reacts toproduce aluminum oxide (Al₂O₃), and liquid iron (Fe), which is a moltenplasma-like substance. The chemical reaction is:

Fe₂O₃+2Al(s)→Al₂O₃(s)+2Fe(l)

As stated above, one or more of the components of the plug 14 is formedfrom a consumable material that burns away and/or loses its structuralintegrity when exposed to the heat and oxygen resulting from the burningof the thermite. The components of the plug 14 that may be formed of theconsumable material should be suitable for service in a downholeenvironment and provide adequate strength to enable proper operation ofthe plug 14. By way of example only, the mandrel 30 and/or the slips 52a and 52 b of the plug can be fabricated of a consumable material, andan example of the latter material is magnesium metal.

After the plug 14 is installed in the wellbore 10, and if it is desiredto remove the plug for the same reasons as indicated in the previousembodiment, the actuator 60 is attached to the end of the string 16, andthe string 16 is lowered into the wellbore 10 until the actuator 60extends above, and in proximity to, the plug 14 and, more particularly,the initiator 38 (FIG. 2). The initiator 38 is activated by thetransmitted wireless signal, or code, from the actuator 60, as describedabove.

Activation of the initiator 38 produces a high current across the abovedescribed bridge wire which generates heat sufficient to ignite, orburn, the material, such as thermite, surrounding the bridge wire, thusproducing heat and oxygen. The consumable components of the plug 14,which in the above example are the mandrel 30 and/or the slips 52 a and52 b, will react with the oxygen in the aluminum oxide (Al₂O₃), causingthe magnesium metal to be consumed or converted into magnesium oxide(MgO), as illustrated by the chemical reaction below:

3Mg+Al₂O₃→3MgO+2Al

A slag is thus produced such that the mandrel 30 and/or the slips 52 aand 52 b no longer have structural integrity and thus cannot carry theload. The engagement of the plug 14 with the casing 12 or the wellbore10 is released and the resulting slag and/or fragments of the mandrel 30and the slips 52 a and 52 b, along with the remaining components of theplug 14, fall to the bottom of the wellbore 10 by gravity.

The string 16 , with the actuator 60 (FIG. 3), is then brought to theground surface by the winch of the rig 18 (FIG. 1). The above-mentionedclosure device associated with the wellhead 22 (FIG. 1) is thenreinstalled over the wellhead 22 and set to prevent any flow ofproduction fluid from the formation and through the wellbore 10 to therig 18.

Thus, as in the previous embodiment, the plug 14 can be placed in thewellbore 10 and activated to seal off the flow of production fluid asdiscussed above and yet can be removed in a relatively simple andinexpensive manner at any indeterminate time.

Variations

It is understood that variations may be made in the foregoing withoutdeparting from the scope of the invention. Non-limiting examples ofthese variations are as follows:

(1) The number and type of the slips 52 a and 52 b and the sealingelement 44 can be varied within the scope of the invention.

(2) The type of electronic signal transmitted from the actuator 60 tothe initiator 38 to activate the initiator 38 can be varied and can begenerated by electrical, acoustical, or magnetic devices, in aconventional manner.

(3) The initiator 38 could be activated by mechanical means such as afishing head attachment that is operated by a hook, or the like,attached to the string 16.

(4) The wellbore 10 could be an open hole completion, sans the casing12, in which case the wellbore 10 would be sealed by the plug 14.

(5) The signal transmitted to the initiator 38 could be transmitted fromthe ground surface.

(6) In the second embodiment disclosed above, components, other than theslips 52 a and 52 b and the mandrel 30 may be fabricated from theconsumable material that loses structural integrity when exposed to heatand an oxygen source.

(7) The consumable components of the plug 14 can be fabricated from amaterial other than magnesium metal.

(8) Conventional blasting caps can be used in place of the bridge wirediscussed above.

(9) The plug 14 can used in other well servicing or well treatmentoperations when temporary plugging of the well is needed such as infracturing operations.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto and theirequivalents.

1. A method for sealing a casing or a wellbore, comprising: providing anexplosive on a sealing plug; lowering the plug into the casing or thewellbore; expanding the plug into engagement with the casing or wellboreto provide a seal; and transmitting a signal to the plug to explode theexplosive and release the engagement.
 2. The method of claim 1 furthercomprising providing an initiator on the plug to receive the signal andto initiate the exploding of the explosive in response to receiving thesignal.
 3. The method of claim 2 further comprising lowering an actuatorinto the wellbore and then transmitting the signal from the actuator tothe initiator.
 4. The method of claim 3 further comprising: lowering theplug into the wellbore by a string; releasing the plug from the string;and removing the string from the wellbore; wherein lowering the actuatorcomprises connecting the actuator to the string and lowering the stringand the actuator into the wellbore.
 5. The method of claim 1 wherein theexplosive is contained in a cord and the method further compriseswrapping the cord around a liner in the plug.
 6. The method of claim 1wherein the explosion disintegrates, or breaks up, at least a portion ofthe plug to release the engagement, and the resulting fragments of theplug fall to the bottom of the wellbore by gravity.
 7. A method forsealing a casing or a wellbore, comprising: providing a sealing plughaving at least one consumable component; lowering the plug into thecasing or the wellbore; expanding the plug into engagement with thecasing or wellbore to provide a seal; transmitting a signal to the plug;and producing heat and oxygen in response to transmitting the signal,wherein the heat and oxygen consumes the at least one component of theplug to cause the plug to release the engagement.
 8. The method of claim7 wherein producing heat and oxygen comprises igniting a material inresponse to the transmission of the signal to cause the material toproduce heat and oxygen.
 9. The method of claim 8 wherein igniting thematerial comprises placing the material in proximity to a wire, andapplying a voltage to the wire to produce heat sufficient to ignite thematerial.
 10. The method of claim 8 further comprising providing aninitiator on the plug to receive the signal and to initiate theproduction of heat and oxygen.
 11. The method of claim 8 wherein atleast one component of the plug is fabricated from a magnesium metalthat consumes in the presence of the heat and oxygen.
 12. The method ofclaim 8 further comprising lowering an actuator into the wellbore andthen transmitting the signal from the actuator to initiate the ignition.13. The method of claim 11 further comprising: lowering the plug intothe wellbore by a string; releasing the plug from the string; andremoving the string from the wellbore; wherein lowering the actuatorcomprises connecting the actuator to the string and lowering the stringand the actuator into the wellbore.
 14. The method of claim 8 whereinthe consumption of the at least one component of the plug causes theplug to lose its structural integrity and release the engagement, andthe consumed component, along with the remaining components of the plug,fall to the bottom of the wellbore by gravity.
 15. A method for sealinga casing or a wellbore, comprising: lowering a sealing plug into thecasing or the wellbore; expanding the plug into engagement with thecasing or wellbore to provide a seal; transmitting a signal to the plug;and causing at least one component of the plug to loose its structuralintegrity in response to transmitting the signal to cause the plug torelease the engagement.
 16. The method of claim 15 wherein an explosiveis ignited in response to transmitting the signal to cause the plug tolose it structural integrity.
 17. The method of claim 16 furthercomprising providing an initiator on the plug to receive the signal andto ignite the explosive.
 18. The method of claim 17 wherein a materialis ignited in response to the transmission of the signal and producesheat and oxygen, and at least one component of the plug is consumed bythe heat and oxygen to cause the plug to lose its structural integrity.19. The method of claim 18 further comprising providing an initiator onthe plug to receive the signal and to initiate the production of theheat and oxygen.
 20. The method of claim 19 wherein at least onecomponent of the plug is fabricated from a magnesium metal that consumesin the presence of the heat and oxygen.
 21. The method of claim 15further comprising lowering an actuator into the wellbore and thentransmitting the signal from the actuator.
 22. The method of claim 21further comprising: lowering the plug into the wellbore by a string;releasing the plug from the string; and removing the string from thewellbore; wherein lowering the actuator comprises connecting theactuator to the string and lowering the string and the actuator into thewellbore.